U.S. patent number 5,330,535 [Application Number 08/052,220] was granted by the patent office on 1994-07-19 for screw-nut for screwing implants together.
This patent grant is currently assigned to Protek AG, Sulzer Brothers Limited. Invention is credited to Walter Moser, Roland Willi.
United States Patent |
5,330,535 |
Moser , et al. |
July 19, 1994 |
Screw-nut for screwing implants together
Abstract
A screw-nut for screwing implants together includes a
thrust-shoulder which projects radially and presses axially against
part of a housing. The screw-nut further includes an internal
threaded portion adapted to fit a corresponding screw part, and a
plurality of members, each mounted onto the side of the
thrust-shoulder facing away from the part of the housing against
which the thrust shoulder presses. These members are adapted to
receive a tool for tightening the screw-nut. A plurality of leaf
springs is included for engaging the housing part. The leaf
springs, the ends of which form latching-in dogs, project, in the
axial direction, from the screw-nut. The leaf springs are
constructed such that, when the thrust-shoulder makes contact with
the housing part, each latching-in dog snaps into a recess in the
housing part in order to prevent loosening of the screw-nut from
the housing part.
Inventors: |
Moser; Walter (Herrenschwanden,
CH), Willi; Roland (Netterbach, CH) |
Assignee: |
Sulzer Brothers Limited
(Winterthur, CH)
Protek AG (Berne, CH)
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Family
ID: |
4192932 |
Appl.
No.: |
08/052,220 |
Filed: |
April 22, 1993 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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848091 |
Mar 9, 1992 |
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Foreign Application Priority Data
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Mar 7, 1991 [CH] |
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00692/91-3 |
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Current U.S.
Class: |
623/20.35 |
Current CPC
Class: |
A61F
2/30721 (20130101); A61F 2/30749 (20130101); A61F
2/38 (20130101); F16B 37/043 (20130101); F16B
41/002 (20130101); A61F 2002/30405 (20130101); A61F
2002/30495 (20130101); A61F 2002/305 (20130101); A61F
2002/30571 (20130101); A61F 2220/0025 (20130101) |
Current International
Class: |
A61F
2/30 (20060101); A61F 2/38 (20060101); F16B
41/00 (20060101); F16B 37/04 (20060101); A61F
2/00 (20060101); A61F 002/38 () |
Field of
Search: |
;623/16,18,19,20 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Isabella; David
Attorney, Agent or Firm: Kenyon & Kenyon
Parent Case Text
This is a continuation of Ser. No. 07/848,091, filed Mar. 9, 1992,
now abandoned.
Claims
What is claimed is:
1. An implant comprising:
a tibia plate which, when in an operative position, settles on a
resected tibia bone to form a platform for an artificial knee, the
tibia plate including a stem receiving recess;
a stem projecting into the stem receiving recess of the tibia
plate, wherein the stem is connected to the tibia plate for
enhancing side-hold and for preventing withdrawal of the tibia
plate, wherein:
a portion of the stem which, when in the operative position,
contacts a lower plane of the tibia plate, consists of a cone with
a small half angle which fits into a cylindrical bore in the tibia
plate, the cylindrical bore including a rounded corner to produce
line contact between the stem and the lower plane of the tibia
plate;
and wherein a clearance exists between the cylindrical bore and the
projecting stem in the direction of an upper plane of the tibia
plate, the clearance being sized to allow the tibia plate to be
substantially inclined out of a position perpendicular to the stem
axis towards the stem axis;
the implant further including a screw-nut inserted from the top of
the plate to press against a shoulder of the plate in an upper
plane of the tibia plate and fixing the stem in the operative
position while allowing the inclination of the tibia plate toward
or away from the stem axis.
2. An implant according to claim 1, wherein a portion of the stem
which, when in the operative position, is located between the upper
and lower planes of the tibia plate has a reduced bending stiffness
relative to the portion of the stem which is located below the
lower plane of the tibia plate to allow the tibia plate to follow
an elastic deformation of the tibia bone by further inclination
with reference to the lower plane.
3. An implant according to claim 1, wherein the screw-nut includes
a thrust shoulder and a plurality of leaf springs for engaging the
shoulder of the tibia plate, each leaf spring projecting in the
axial direction away from the screw-nut wherein the end of each
leaf spring forms a latching-in dog which, when the thrust shoulder
of the screw-nut contacts the shoulder of the tibia plate, snaps
into a recess in the cylindrical bore of the tibia plate to prevent
loosening of the screw-nut from the tibia plate.
4. An implant according to claim 3, wherein each latching-in dog
includes a run-up face which, upon the leaf spring being run into
the cylindrical bore of the tibia plate, is prestressed in order to
execute a latching-in motion, upon the thrust-shoulder making
contact with the housing part.
5. An implant according to claim 1, wherein the stem includes a
screw portion and the screw-nut includes a corresponding internal
threaded portion, wherein the length, in the axial direction, of
the internal threaded portion is greater than the distance from the
point of contact between the tibia plate and the leaf springs so
that deformation of the leaf springs may be performed by a screwing
motion engaging the internal threaded portion with the
corresponding screw part so that the screw part does not project
axially beyond the screw-nut in the final mounted position.
6. An implant according to claim 3, wherein a clearance in the
axial direction exists between each of the latching-in dogs and a
counterface on the tibia plate such that the screw-nut may be
turned with respect to the tibia plate part while latched into the
tibia plate.
Description
The invention deals with a screw-nut for screwing implants
together, having a thrust-shoulder which projects radially and
presses axially against part of a housing, and having an internal
thread which fits a screw part and members moulded onto the side
facing away from the housing part in order to insert a tool for
tightening the screw-nut.
In contrast to the rigid connections of machine construction it
would, in the case of certain connections between components of
implants, be highly advantageous if micro-movements between the
components were possible in order to take into account the
elasticity of the bone tissue growing in and the intermediate
alterations in the bone tissue. Thus the EP-OS 0 333 642 A1 shows
an anchoring plate for the bearing areas of a tibia, which is
connected to anchoring studs through a screw connection which my be
loosened from outside.
One disadvantage of the connection lies in the fact that--because
of the securing of the screw connection--it is made rigid and
reproduces movements of the tibia plate with respect to the bone
tissue in an unrestricted manner at the anchoring studs.
Here the invention creates a remedy. It solves the problem of
securing, in the tibia plate, an anchoring stud which is anchored
in the bone tissue, in such a way that, through a screw connection,
that micro swinging movements can take place between the anchoring
studs and the tibia plate.
In accordance with the invention, the problem is solved by leaf
springs, projecting in the axial direction, being moulded onto the
screw-nut and ending in latching-in dogs. In addition, the fact
that, with the thrust-shoulder making contact with the housing
part, the latching-in dogs snap into a recess in the housing part
in order to prevent loosening of the screw-nut from the housing
part.
The advantage of the invention consists in the fact that, for a
limited range with the occurrence of a bending moment in the
clamping of the anchoring stud, a swinging movement occurs which
grows with the bending moment without the members for screwing
together the tibia plate being able to loosen in the long term.
The invention is described below with the aid of an embodiment.
There is shown diagrammatically in:
FIG. 1 - a section through the anchoring of an anchoring stud in a
tibia plate by a screw connection; and
FIG. 2 - the perspective of a screw-nut shown in FIG. 1.
The Figures show a screw-nut for screwing implants together, having
a thrust-shoulder which projects radially and presses axially
against part of a housing, and having an internal thread which fits
a screw part and members moulded onto the side facing away from the
housing part in order to insert a tool for tightening the
screw-nut. In accordance with the invention, leaf springs which
project in the axial direction are moulded onto the screw-nut and
end in latching-in dogs. Upon pressing the screw-nut into the
housing part, with the thrust-shoulder making contact, the
latching-in dogs snap in to a recess in the housing part in order
to prevent loosening of the screw-nut from the housing part.
As shown in FIG. 1, an anchoring stud is inserted in a cylindrical
hole drilled in a part 5 of a housing made as a tibia plate and is
secured axially by a screw-nut 1. The stud is seated by a short
taper part 16 along a line contact 18 area with a rounded corner 19
at the entrance to the drilled hole whilst the cylindrical part 17
adjoining it exhibits play with respect to the drilled hole in
order to be able to perform small swinging movements referred to
the clamping at the taper part 16. The anchoring stud ends at the
outside of the tibia plate as a threaded bolt with a screwed part
12 upon which the screw-nut 1 rides by the internal thread 9.
In FIG. 2 a screw-nut 1 may be seen, from which four leaf springs 2
project in the axial direction to end in latching-in dogs 3, these
latching-in dogs having, in the direction of insertion, oblique or
rounded run-up faces 8 and, in the direction of extraction, steep
latching-in faces.
Upon entering the screw-nut 1 into the part 5 of the housing, the
leaf springs are prestressed by the running-up faces 8 running up
radially inward until the latching-in dogs--at the latest as the
thrust-shoulder 4 makes contact--snap in to a recess 6 in the part
5 of the housing. With the thrust shoulder 4 resting against the
housing part 5 a clearance 13 in the direction of the axis 7 of the
screw results between the latching-in dogs 3 and a counterface on
the housing part 5, which is so dimensioned that the latched-in
screw-nut 1 is supported to be able to turn in the housing part 5.
On the side facing away from the housing part the screw-nut 1 has
shaped members 14 in the form of slots in which a tool can engage
in order to tighten the nut. Even if upon first screwing the
screw-nut 1 onto the anchoring stud it has been pulled tight it is
not assumed that the axial prestress is maintained. Micro movements
and settling in the taper part loosen the connection between the
screw part 12 and internal thread 9, so that the planned swinging
movements of the anchoring stud with respect to the housing part 5
can take place without the screw-nut 1 loosening inadmissibly from
the housing part 5, thanks to the latching-in.
The screw-nut 1 may be premounted in the housing part 5 by being
pressed axially into the housing part until the thrust shoulder 4
seats. After the insertion of the anchoring stud in the tibia part
the housing part 5 made as the tibia plate is run in over the screw
part 12 until the internal thread 9 seats and by turning the
screw-nut 1 is brought along until in its final position.
Another possibility consists in inserting the anchoring stud almost
home, mounting the tibia plate over the screw part 12 until the
taper part 16 engages and inserting both parts together as far as
the final position. Then the screw-nut 1 is mounted and turned in
along the screw part 12 until the thrust-shoulder 4 strikes against
the housing part and latching-in by the latching-in dogs 3 takes
place. In FIG. 1 the screw part 12 terminates at the outer face of
the tibia plate. The counterface for the thrust-shoulder 4 is set
back inside by a length 10. The axial distance 11, between the
internal thread 9 and the point of contact on the run-up faces 8
which first runs up against the housing part 5, is clearly less
than the length 10 so that a movement pressing inward is effected
through the internal thread 9 engaging and a torque being applied
to the screw-nut 1. The turning in of the screw-nut is effected by
an auxiliary tool which may be centered on a bevel 15 on the
screw-nut and engages in the slots 14 in order to transmit the
necessary torque.
* * * * *